Swelling of Wustite Pellets during the Reduction with CO-CO₂ Mixtures Containing Small Amounts of Sulphur

Abstract

Swelling of wustite pellets during the reduction with CO-CO² mixtures containing COS at low partial pressure was investigated in the temperature range from 800 to 1 000°C.
When the ratio P_COS/P_CO in reducing gas was lower in 10^-2 than the equilibrium ratio between iron and iron sulphide, the abnormal swelling of pellets was observed as accompanied with the formation of fibrous iron. This range of the gas ratio was seemed to be independent of the presence of CaO and K₂O in wustite.
CaO and K₂O dissolved in wustite did not directly induce the abnormal swelling, but the gaseous sulphur enhanced the abnormal swelling more greatly due to the coexistence of oxide additive in wustite.
Two reasons for the favorable formation of fibrous iron induced by the gaseous sulphur were based on the sulphur adsorption on the solids. One is that sulphur diminishes the number of sites for the iron nucleation due to its adsorption at defects on wustite surface. The other is that sulphur induces upward growth of iron, inhibiting lateral growth of iron due to its adsorption on active iron surface.